There is great interest in field emission electron sources, often referred to as field emission materials or field emitters, for use in a variety of electronic applications, such as in flat panel display monitors, television displays, vacuum electronic devices, emission gate applications, klystrons, vacuum microelectronics applications, and the like.
The field of vacuum microelectronics began with the development of a flat display using microscopic molybdenum cones singly or in arrays (so-called Spindt emitters). Further work led to investigations using arrays consisting of silicon microtips, wherein silicon is oxidized followed by patterning of the oxide and selective etching to form silicon tips, which can act as cold cathodes for a field emission display. Development of new materials for cold cathodes has led to cathode arrays constructed from silicon, gallium arsenide, molybdenum, nickel, platinum, iridium, diamond, and conducting carbides.
Generally, the phenomenon of field emission refers to emission of electrons from a conductive material under the influence of an applied electric field. When a conductive material, as a cathode, is placed proximately to an anode under a high vacuum, and an electric potential is applied across the gap, the resulting flow of electrons from cathode to anode via field emission completes an electric circuit and results in the generation of an electric current.
Typically, field emission devices are comprised of arrays of sharp pointed tips from which electrons are emitted. For example, U.S. Pat. No. 6,620,640 describes a process comprising patterning and doping of a silicon substrate. The doped silicon substrate is then anodized. Where the silicon substrate is doped, spires of porous silicon are formed. These sharp spires or asperities are useful as emitter tips.
An impediment to development of such devices lies in the manufacturing difficulties that are necessary to overcome in order to fabricate the arrays of tips. Efforts to overcome the difficulties posed by such technology has led to the discovery that materials such as diamond-like films or small conductive particles, particularly carbon nanotubes, either arranged in arrays or distributed in a matrix, can be field emitters. U.S. Pat. No. 6,250,984 describes a process for fabricating carbon nanotube field emitter structures. The carbon nanotubes are mixed with metal particles and consolidated into a compact, and the compact is then sectioned to expose a substantial number of nanotube ends. A layer of the metal is selectively etched from the sectioned surface, exposing nanotubes protruding from the surface. The resulting structure purportedly provides a device having improved field emission properties.
Despite the advances that have been made in exploitation of field emitting properties of particulate materials, several technological hurdles remains before such field emitters can be utilized in practical devices. Typically, field emitters comprising carbon nanotubes are fabricated microdevices consisting of aligned preformed carbon nanotubes retained in a support, or consisting of carbon nanotubes grown into a preformed support. There remains a need for field emitting materials that are simply prepared, do not require complex support elements and methods of fabrication, and are stable under typical operating conditions.
The invention provides such a field emitting material and methods for its production and use. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.